Potentiodynamic Anodic Polarization Research Articles

Effect of Cold Working on Corrosion Fatigue Behavior of Austenitic Stainless Steel in Acidified Chloride medium

Nitrogen is one of the most important alloying elements in alloy steels and even in small amounts can improve their properties. Because of its favorable properties, high performance nitrogen containing austenitic stainless steels are currently being developed for an advanced application that requires high strength along with better corrosion and wear resistance. The present study investigate the effects of cold work (CW) on the microstructure and corrosion fatigue (CF) resistance of AISI Type 316 LN stainless steel containing 0.11 wt. % nitrogen using microscopic, electrochemical and surface analytical methods. Potentiodynamic anodic polarization experiments were carried out in two chloride concentrations (1 M NaCl) and (5 M NaCl + 0.15 M Na2SO4) indicated that pitting potential (Epit) and passivity range drastically decreased with increase in chloride concentration and increased deformation from 0 to 20% CW. In 5 M NaCl + 0.15 M Na2SO4, corrosion resistance (Rp) decreases with an increase in cold work due to increased susceptibility of the passive film towards dissolution due to increase in dislocation density. CF behaviour of AISI Type 316LN SS with 0.11 wt.% nitrogen was studied in acidified 5 M NaCl + 0.15M Na2SO4 solution at a stress ratio (R) of 0.5 and a frequency (η) of 0.1 Hz with varying mean stress (σmean) and open circuit potential was monitored throughout till the failure of the specimen occur. Based on in-situ electrochemical measurements during corrosion fatigue tests, the shift in potential indicates the crack initiation process. The S-N curve of fatigue life (Nf) vs. stress amplitude was also generated. This study showed that the CF resistance increases with an increase in cold work and the number of cycles to failure and critical cracking potential decreases with increasing mean stress. The crack initiation and propagation show a transgranular mode in all the tested conditions.

Corrosion Resistance of High Temperature Plasma Nitrided X12CrMoWVNbN10-1-1 Martensitic Stainless Steel

The X12CrMoWVNbN10-1-1 martensitic stainless steel was subjected to plasma nitriding at an increased temperature of 550 °C for 15 h and compared to untreated one. The microstructure and microhardness of the untreated and nitrided stainless steel were evaluated. The corrosion properties of the untreated and plasma nitrided steel samples were evaluated using the anodic potentiodynamic polarization tests in neutral 2.5% NaCl deaerated solution. The results showed that plasma nitriding process on the X12CrMoWVNbN10-1-1 stainless steel produced a nitride layer consisting of compound layer and a nitrogen rich diffusion layer. Plasma nitriding process significantly increased the surface hardness of the martensitic stainless steel but also decreased the corrosion resistance of the X12CrMoWVNbN10-1-1 stainless steel. The pitting was evaluated, and the pitting coefficient was calculated. During electrochemical corrosion tests, the nitrided steel showed lower (more negative) corrosion potentials, higher current densities and greatly increased corrosion rates and pitting.

Effects of plastic strains on passivation behavior of different austenitic stainless steel grades

This paper focused on effect of strain on stability of passive film in three different grades of austenitic stainless steels. These were Sanicro 28TM, AISI 316 L and AISI 304 L steels. These specimens were subjected to unidirectional cold rolling and achieved true strain was 0.26 and 0.58. Potentiodynamic anodic polarization tests were carried out for all specimens in different test solutions. The changes in anodic polarization parameters were recorded. The deformed microstructures were characterized by using electron backscattered diffraction (EBSD). Aim of this study was to characterize chromium oxide (Cr2O3) by Fourier transform infrared spectroscopy (FTIR)-imaging. Further, an attempt was made to combine EBSD and FTIR-imaging for direct microstructural correlation.

Effect of target composition on the microstructural, mechanical, and corrosion properties of TiAlN thin films deposited by high-power impulse magnetron sputtering

Ti1−xAlxN thin films were deposited using reactive high-power impulse magnetron sputtering on silicon Si (100), tungsten carbide (WC-Co), and SUS304 substrates using three metallurgical TixAly alloy targets with Al/(Al + Ti) atomic ratios of 0.19, 0.36, and 0.57. A fixed duty cycle of 1% and a N2/Ar ratio of 15.8% was used. The current–voltage characteristics of the TixAly alloy targets were first investigated. Then, the microstructural evolution and the mechanical and corrosion properties of the as-deposited Ti1−xAlxN thin films were analysed by scanning electron microscopy, grazing incident X-ray diffractometry, X-ray photoelectron spectroscopy, transmission electron microscopy, nanoindentation, and anodic potentiodynamic polarisation tests. The power density of 1.86 kW/cm2 achieved with the square-like power output wave obtained in the constant current mode was higher than the 1.37 kW/cm2 power density obtained with the triangular-like power output wave. The deposition rates of the Ti1−xAlxN thin films increased from 13.4 to 28.6 nm/min with an increasing alloy target Al/(Al + Ti) atomic ratio due to the higher sputter yield of Al than Ti. The Al/(Al + Ti) atomic ratio of the alloy target determines the structure, which changed from a highly preferred TiN (111) orientation (Al/(Al + Ti) ratio = 0.19) to a nanocomposite structure (Al/(Al + Ti) ratio = 0.57). The nanoindentation results indicated that the highest hardness and elastic modulus values of the Ti1−xAlxN thin films were 33.3 GPa and 405.9 GPa, respectively, obtained using the Al/(Al + Ti) = 0.19 alloy target. In addition, the friction coefficients of the Ti1−xAlxN thin films were between 0.68 and 0.77. However, the potentiostatic polarisation measurements showed that the amorphous TiAlN films exhibited the highest corrosion resistance in 3.5% NaCl solution, as the corrosion resistance of the Ti1−xAlxN coatings increased as the Al/(Al + Ti) atomic ratio increased.

Corrosion Study on Laser Shock Peened 316L Stainless Steel in Simulated Body Fluid and Chloride Medium

In the present work, corrosion behavior of laser shock peened 316 L stainless steel was evaluated and compared with unpeened specimen in Hank solution (simulated body fluid) and chloride medium. Laser shock peening (LSP) was used for surface modification using Q-switched Nd-YAG laser. In the corrosion study, different electrochemical experiments such as open circuit potential (OCP)-time measurements, potentiodynamic anodic polarization, electrochemical impedance spectroscopy (EIS) measurements were performed in 0.5 M NaCl and Hank solution to examine the corrosion resistance of unpeened and laser peened 316 L SS specimens. The results of corrosion study demonstrated that LSP improved the pitting corrosion resistance despite marginally higher roughness (Ra = 1.01 μm) for laser peened surface than unpeened surface (Ra = 0.54 μm). Improvement in pitting corrosion resistance was indicated by ennoblement of OCP, more noble (anodic) value of pitting potential (Epit) and lower corrosion current density (Icorr). Conductivity and pH of NaCl and Hank solution increased after every polarization experiments which indicate the ionic dissolution during corrosion experiments. Qualitative analysis of Nyquist plots obtained from electrochemical impedance spectroscopy (EIS) results also showed higher arc radius (higher polarization resistance) for laser peened specimen than unpeened, which is indicative of more protective passive film and hence improved corrosion resistance. Further, microstructural examination after polarization experiments in both NaCl and Hank solution showed less pitting sites in laser peened specimens than unpeened surfaces. These microstructural observations are in line with the results obtained in polarization experiments. The results of the study are important with respect to medical implants and their biocompatibility in the human body.

Effects of Severe Plastic Deformation and Interstitial Carbon on Corrosion Resistance of Steel

For the improvement of mechanical properties of steels, nanocrystallization is a center of interest. Nanocrystallization greatly influences on the mechanical properties such as tensile strength, ductility, and wear resistance. Severe plastic deformation (SPD) is one of the effective methods to generate the nanocrystalline structure. It was reported that nanocrystallization also affects corrosion behavior of steels. When the grain size of stainless steels is less than 1 μm, it would appear that the grain boundaries act as barriers against the growth of pitting corrosion1). Interstitial carbon atoms also affect the corrosion behavior2). In this study, the SPD layers were fabricated on Fe plates by ball-milling, and electrochemical measurements were conducted to investigate the corrosion behavior of the SPD layers. Planetary ball-milling was applied to fabricate the SPD layers on Fe and stainless steel plates. The Fe and type 304 stainless steel plates were polished by SiC paper through a 1500 grid and put into a stainless steel pot with Fe powders, and mechanical alloying of Fe and C powders was accomplished. Grinding balls were made of stainless steel. In the milling process, the SPD layers of Fe-C alloy were fabricated on the Fe and stainless steel plates. To investigate the effect of the carbon concentration, the amount of the carbon powders put into the pot was changed. Potentiodynamic anodic polarization curves were measured in deaerated H3BO3-Na2B4O7-1 mM NaCl solution (pH 8.0) at 298 K to elucidate the influence of the SPD and the carbon concentration on the corrosion resistance of the Fe-C steels. With the exception of the electrode area (ca. 5 mm × 5 mm), the surfaces of the specimen were coated with an epoxy resin and paraffin. The measurements were performed in a conventional three electrode cell. The reference electrode was Ag/AgCl (3.33 M KCl) and the counter electrode was a Pt plate. The results of potentiodynamic anodic polarization for the SPD layers on the Fe plates are shown in Fig. 1. In the case of pure Fe, the increase of the anodic current density at ca. -0.5 V was due to the anodic oxidation and/or dissolution of Fe. In the potential range of -0.3 to 0 V, the current density decreased by passivation. And then, the current density drastically increased. This appeared to be attributed to localized corrosion. On the other hand, at around -0.5 V, the current densities for Fe-0.1mass%C and Fe-0.5mass%C were higher than that of pure Fe. However, the passivation current density of Fe-0.5mass%C specimen was the lowest. Therefore, the increase of carbon concentration possibly causes the improvement of corrosion resistance.

The Role of Pitting at Mns Inclusions in Intergranular Corrosion of Sensitized Type 304 Stainless Steel in NaCl Solution

The degree of sensitization and susceptibility of intergranular corrosion of austenitic stainless steels are properly evaluated from immersion testing in acidic solutions as rapid screening methods. However, most of stainless steels are used in near-neutral pH environments, and the typical corrosion morphology in these environments is pitting. Acidification is known to occur inside pits due to the hydrolysis reaction of dissolving metal ions. Under practical service conditions around neutral pH such as seawater and river water, pitting is assumed to be closely related to the initiation of intergranular corrosion. It is well-known that non-metallic inclusions, such as MnS, act as the initiation sites for pitting of stainless steels. Chiba et al. demonstrated that a small inclusion-free area on Type 304 indicated superior pitting corrosion resistance even in 3 M NaCl. 1) It would appear that MnS inclusions strongly affect pitting and intergranular corrosion of sensitized stainless steels. To clarify the role of pitting at MnS inclusions in intergranular corrosion of sensitized Type 304 stainless steel (sensitized at 923 K), in situ observations were carried out during micro-scale anodic polarization in 1 M NaCl (pH 5.4). Micro-scale potentiodynamic anodic polarization was performed for a small area with a MnS inclusion at a sensitized grain boundary. Intergranular corrosion was initiated from the pit that was generated at the MnS inclusion located at the sensitized grain boundary. Acidification inside the pit probably caused intergranular corrosion due to the transition from passive to active state. In 1 M NaCl, the depassivation pH values at the sensitized grain boundary with and without MnS inclusions were 1.0 and 0.4, respectively. It is likely that the dissolution of MnS accelerates the depassivation and promote the initiation pf intergranular corrosion. The dissolution products from MnS are supposed to accelerate depassivation of Cr-depleted regions. 1) A. Chiba, I. Muto, Y. Sugawara, N. Hara, J. Electrochem. Soc., 160, C511-C520 (2013).

In Situ Microscopic Observation of Pitting Corrosion Behavior of A1050-O

Al-Fe alloys are used for containers, cables, and window flashings because of their high formability, high strength/weight ratio, and easy machinability. The mechanical properties of Al-Fe alloys have been improved by controlling the morphology of precipitates, however, there have been reports that some precipitates are the sites for pit initiation. The precipitates are known to have a function as the sites for oxygen reduction reaction which results in local alkalization. Due to the local alkalization, Al-matrix around the precipitates dissolves, and trenches are formed around the precipitates. It is known that pits are readily initiated in the trenches, the corrosion behavior from trench formation to pit initiation is still unclear. In this research, in situ observations on the dissolution behavior around precipitates was performed using a micro-electrochemical system, and the effect of pH and precipitate compositions on pitting were determined. In this study, A1050-O was used as the specimens. The specimen surface was polished down to 0.25 µm with a diamond paste and cleaned ultrasonically in ethanol before electrochemical measurements were taken. Two types of the precipitates, AlxFe and AlxFe2Si, were observed in A1050-O. Anodic polarization curves were measured in 0.1 M NaCl (pH 6.0, naturally aerated). The polarization was started from -0.9 V vs. Ag/AgCl (3.33 M KCl), and the scanning rate was 23 mV / min. A stable pit was initiated at -0.4 V, and it was confirmed that the pit was generated at a precipitate. Using a micro-electrochemical system, potentiodynamic anodic polarization curves for a small area with each type of the precipitate were measured in 0.1 NaCl (pH 6.0, naturally aerated) at 298 K. The electrode area was ca. 5000 µm2. The surface appearance of the precipitate was observed during the anodic polarization using a water immersion objective lens. A deep trench was formed around the AlxFe2Si precipitate in the potential range from -0.86 to -0.65 V. Around the AlxFe precipitate, no trench was formed. It was found that the pit was initiated in the trench around the AlxFe2Si precipitates. In order to analyze the corrosion behavior of A1050-O, open circuit potentials were measured in 0.1 M NaCl (pH 6.0, naturally aerated) and 0.1 M NaCl-containing citrate buffer (pH 6.0, naturally aerated) solutions. Fig. 1a shows the time variation of the open circuit potentials of A1050-O in each electrolyte. In 0.1 M NaCl, the potential increased to ca. -0.65 V. On the other hand, in the 0.1 M NaCl-containing citrate buffer solution, the potentials decreased to ca. -0.83 V. Fig. 1b and 1c show the optical micrographs of the AlxFe2Si precipitate after the immersion. Even though a deep trench was formed around the precipitates in 0.1 M NaCl, no trench was formed around the precipitates in 0.1 M NaCl-containing citrate buffer solution. The depassivation pH of pure Al (99.999%) was measured to elucidate the corrosion behavior from trench formation to pit initiation. Electrolyte was 0.1 M NaCl (naturally aerated), and the pH was adjusted with NaOH solution. The open circuit potential decreased with pH from pH 6 to 13, but the open circuit potential increased at pH 14. After the measurement, the specimen surface was corroded. It is suggested that the surface film on pure Al was stable from pH 6 to 13, and that the open circuit potential decreased due to the pH dependence of the electrode potential of hydrogen generation reaction. At pH 14, the surface film dissolved, and bare Al was exposed to the solution. Because oxygen reduction reaction readily occurs on the bare Al, predominant cathodic reaction changed from hydrogen generation to oxygen reduction. The increase in the open circuit potential in 0.1 M NaCl (Fig. 1a) indicates the exposure of bare Al-matrix. In this research, it was found that the citrate buffer prevent the local alkalization and the trench formation around the precipitates. Figure 1

Competent inhibitor for the corrosion of zinc in hydrochloric acid based on 2,6-bis-[1-(2-phenylhydrazono)ethyl]pyridine

A novel compound, 2,6-bis-[1-(2-phenylhydrazono)ethyl]pyridine (BPEP), was synthesized and confirmed by NMR and IR spectroscopy. BPEP was examined as an inhibitor for the corrosion of zinc electrode in 1.0 M HCl. The inhibition efficiency of BPEP was assessed through various techniques such as hydrogen evolution, galvanostatic polarization, potentiodynamic anodic polarization, and electrochemical impedance spectroscopy. The inhibiting action of BPEP was explained in terms of the formation of a stable complex between zinc ions and BPEP and then adsorbed onto the zinc surface. The formation of the complex was established by FT-IR spectroscopy. A conductometric titration indicated that the stoichiometry of Zn+2:BPEP (metal:ligand) is 1:1. The adsorption follows the Langmuir isotherm. The Galvanostatic polarization measurements have shown that the BPEP molecule acts as a mixed-type inhibitor. The pitting potential shifted in the noble direction, indicating that the inhibition of pitting corrosion of zinc in the presence of BPEP.The activation energy and themodyanamic parameters of the adsorption process were calculated and have been explained.

Capacitance characteristics of carbon-based electrochemical capacitors exposed to heteropolytungstic acid electrolyte

A Keggin-type heteropolytungstic acid, H3PW12O40, is evaluated as new high ionic conductivity aqueous electrolyte of potential interest for electrochemical capacitors, with enhanced safety and low environmental concern. For the performance evaluation, two types of electrode materials have been selected, i.e. mesoporous multi-walled carbon nanotubes and microporous activated carbons. To address the influence of changes in the porous structure and surface properties on capacitors performance, the materials have been subjected to additional oxidation treatment under liquid or gas phase conditions. The electrochemical parameters of two-electrode cells were evaluated from a series of voltammetric, galvanostatic, constant power, and AC impedance measurements and compared with those obtained for conventional H2SO4 electrolyte. It has been shown that due to the size of the heteropolytungstate anion (exceeding 1 nm), the selection of carbon electrode materials in terms of appropriate porous structure and wettability is a key factor in avoiding capacitance limitations. As a result, the specific capacitance, energy density as well as the rate capability of H3PW12O40 supported capacitors may approach the performance of conventional H2SO4-based systems. Furthermore, the potentiodynamic anodic polarization tests and post-mortem scanning electron microscopy analysis confirmed a higher corrosion resistance of 316 L type steel in the presence of H3PW12O40 solution, in comparison to the conventional H2SO4 electrolyte. It enables stable capacitor performance upon utilization of low cost non-noble current collectors which was evaluated during galvanostatic cycling (13 000 cycles) and accelerated ageing by potentiostatic floating during 120 h.

Anisotropy of corrosion and environmental cracking in AA5083-H128 Al-Mg alloy

The effects of sensitization (175 °C for 100 h) and microstructure anisotropy on corrosion and environmental cracking of AA5083-H128 have been studied using immersion tests, electrochemical experiments and slow strain rate tests (SSRT). Pitting corrosion attack is observed for as-received (AR) and sensitized polished surfaces after immersion in 0.6 M NaCl solution at open circuit potential and is strongly dependent on the amount and distribution of intermetallic particles, including Mg-rich phases resulting from sensitization, as well as pre-existing anodic Mg-rich and cathodic (Mn, Fe)-rich particles. Anodic potentiodynamic polarization experiments indicate that sensitization increases the activity of the surface with a negative shift in corrosion potential and an increase in anodic reaction kinetics. SSRT tests show that samples orientated along the short transverse (S) direction exhibit the largest susceptibility to intergranular stress corrosion cracking (IGSCC), followed by samples with transverse (T) orientation, and then samples with longitudinal (L) orientation. Serrated stress–strain response and flow instability, referred to as the Portevin-Le Chatelier (PLC) effect, is exhibited in SSRT curves, and is more pronounced in L-orientated samples compared to T- and S-oriented samples. The effects of microstructure anisotropy and sensitization on the environmental cracking and the PLC effect are discussed.

Weld joint design and thermal aging influence on the metallurgical, sensitization and pitting corrosion behavior of AISI 304L stainless steel welds

Experimental investigations were carried out to study the influence of weld joint design and post weld thermal aging treatments on the metallurgical, intergranular and pitting corrosion behavior of AISI 304L stainless steel welded joints. 10 mm thick linear weld joints were fabricated using gas metal arc welding process using single-V and double-V joint design with an average heat input of 503.42 J/mm and 562.78 J/mm respectively. Thermal aging of these welds was carried out at 750 °C for 0.5 h and 4 h, and the cooling media used was furnace, air and water quench (used separately for each specimen), so as to induce variable degree of carbide precipitation in different zones of these welds. Microstructural studies revealed that the extent of carbide precipitation was more in case of welds made using double-V joint design as compared to single-V joint welds. Degree of sensitization (DOS) and pitting performance of these welds evaluated using double loop electrochemical potentiokinetic reactivation (DLEPR) technique and potentiodynamic anodic polarization technique respectively, further showed that single-V joint performed better in terms of corrosion properties owing to lesser precipitation as compared to the double-V joint. This study shows that in comparison to double-V joint, single-V joint design can prove to be an important part of fabrication procedures where service conditions demand better corrosion properties of these welds.

Effect of Low-Temperature Sensitization on the Corrosion Behavior of AISI Type 304L SS Weld Metal in Simulated Groundwater

The manuscript presents the investigations carried out on the effect of low-temperature sensitization (LTS) of 304L SS weld metal on its corrosion behavior in simulated groundwater, for its application as a canister material for long-term storage of nuclear vitrified high-level waste in geological repositories. AISI type 304L SS weld pad was fabricated by multipass gas tungsten arc welding process using 308L SS filler wire. The as-welded specimens were subsequently subjected to carbide nucleation and further to LTS at 500 °C for 11 days to simulate a temperature of 300 °C for 100-year life of the canister in geological repositories. Delta ferrite (δ-ferrite) content of the 304L SS weld metal substantially decreased on carbide nucleation treatment and further only a marginal decrease occurred on LTS treatment. The microstructure of the as-welded consisted of δ-ferrite as a minor phase distributed in austenite matrix. The δ-ferrite appeared fragmented in the carbide-nucleated and LTS-treated weld metal. The degree of sensitization measured by double-loop electrochemical potentokinetic reactivation method indicated an increase in carbide nucleation treatment when compared to the as-welded specimens, and further increase occurred on LTS treatment. Potentiodynamic anodic polarization investigations in simulated groundwater indicated a substantial decrease in the localized corrosion resistance of the carbide-nucleated and LTS 304L SS weld metals, when compared to the as-welded specimens. Post-experimental micrographs indicated pitting as the primary mode of attack in the as-welded, while pitting and intergranular corrosion (IGC) occurred in the carbide-nucleated weld metal. LTS-treated weld metal predominantly underwent IGC attack. The decrease in the localized corrosion resistance of the weld metal after LTS treatment was found to have a direct correlation with the degree of sensitization and the weld microstructure. The results are detailed in the manuscript.

Defining the Post-Machined Sub-surface in Austenitic Stainless Steels

Austenitic stainless steels grades, with differences in chemistry, stacking fault energy, and thermal conductivity, were subjected to vertical milling. Anodic potentiodynamic polarization was able to differentiate (with machining speed/strain rate) between different post-machined sub-surfaces in SS 316L and Alloy A (a Cu containing austenitic stainless steel: Sanicroe 28™), but not in SS 304L. However, such differences (in the post-machined sub-surfaces) were revealed in surface roughness, sub-surface residual stresses and misorientations, and in the relative presence of sub-surface Cr2O3 films. It was shown, quantitatively, that higher machining speed reduced surface roughness and also reduced the effective depths of the affected sub-surface layers. A qualitative explanation on the sub-surface microstructural developments was provided based on the temperature-dependent thermal conductivity values. The results herein represent a mechanistic understanding to rationalize the corrosion performance of widely adopted engineering alloys.

Interference film grown on stainless steel by pulsed current process using chromium free vanadate solution

Deposition of interference film is an alternative way for the formation of colored protective layers on the surface of stainless steels for decorative applications. The process involves growth of a chromium oxide film by electrochemical methods using in general sulphochromic solutions. However, it is well known that chro-mic acid contains Cr(VI), which is highly toxic, demanding special effluent treatments in order to avoid envi-ronmental pollution. The aim of the present work is to evaluate alternative chromium free solutions for color-ation of stainless steel by an electrochemical method as a trial to avoid the Cr(VI) presence to achieve an environmentally friendly process. The morphology and corrosion resistance of the conversion coatings ob-tained from sodium vanadate solution were comparatively evaluated with a sample coloured in a sodium mo-lybdate solution containing chromium and in a sulfochromic solution currently used in industrial coloration process. The corrosion behaviour of the colored samples was evaluated by using anodic potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The steel colored in a solution containing chromium and molybdenum ions showed the lowest corrosion resistance and a more porous and heterogene-ous film than the other steel samples colored using vanadate and sulfochromic solutions. An electrochemical processing using a sodium vanadate solution can be a chromium free alternative for industrial application. Keywords: interference film, Cr(VI), anodic polarization, colored stainless steel, EIS, FESEM.

Effects of solution treatment on mechanical properties and corrosion resistance of 4A duplex stainless steel

Abstract In this study, 4A duplex stainless steels were prepared via remelting in an intermediate frequency furnace and subsequently solution treated at different temperatures. The effects of solution treatment on the mechanical properties and corrosion resistance of 4A duplex stainless steel were investigated. Microstructures were characterized via optical microscopy and scanning electron microscopy. The mechanical properties were evaluated via hardness test, tensile test, and impact test experiments. The point corrosion resistance was studied via chemical immersion and potentiodynamic anodic polarization. The results showed that with increasing solution temperature in the range of 1 223 – 1 423 K, the tensile strength and hardness first decreased and then increased, and minimum values were obtained at 1 323 K. The σ phase precipitated at the boundaries of the α/γ phases in samples solution treated at 1 223 K, decreasing both impact energy and pitting potential of the experimental steels. When experimental steels were solution treated at 1 373 K for 2 h, a suitable volume fraction of α/γ was uniformly distributed throughout the microstructure, and the steels exhibited optimal mechanical properties and pitting corrosion resistance.

Effects of zinc powder addition to Villa Gloss and Silka Lux marine enamel paints on corrosion resistance of mild steel

The anti - corrosion properties of paints can be optimised when adequate proportion of the paint constituents are used. Effect of zinc powder addition to Villa Gloss and Silka Lux Marine Enamel paints on corrosion resistance of mild steel was studied. Quantitative Analysis and Potentiodynamic Polarisation Technique were used to evaluate the samples. The results indicate that zinc powder addition between 15 and 25 % signifi cantly reduced the corrosion rate. The corrosion rate stabilized at approximately 0.10 mmpy when zinc powder added was above 15%, independent of the exposure time. Potentiodynamic anodic polarization curves of the samples immersed in seawater showed that sample with 25% zinc powder addition exhibited highest corrosion potential and the least corrosion current density . Microstructural analysis of the samples also revealed the presence of pitting corrosion at the surfaces of the samples and their geometry, v olume fraction and distribution vary with the zinc powder addition. Keywords : zinc powder, inhibition efficiency, potentiodynamic, weight loss, corrosion rate, pit corrosion

Corrosion Inhibition of Carbon Steel in 1 M Hydrochloric Acid using Some Pyrazolo[3,4-d]Pyrimidnone Derivatives

The inhibiting effect of three compounds of pyrazolo[3,4-d] pyrimidnone derivatives toward the corrosion of carbon steel in 1.0M HCl solution was investigated using galvanostatic and potentiodynamic anodic polarization techniques. The rise of the concentration of the inhibitors and decreasing the temperature led to the greater of inhibition efficiency. The inhibiting action of these compounds was explicated on the footing of its adsorption on the carbon steel surface. The adsorption operation of these compounds was obeyed Langmuir isotherm. There is only one anodic peak during the anodic cyclic voltammogram This peak was elucidated due to the active dissolution of Fe as Fe2+. The percentage inhibition efficiency was computed from the values of peak current density.There is a good convention between the values of the percentage inhibition efficiency gained from the diverse techniques.These compounds inhibit the pitting corrosion of carbon steel by shifiting the pitting corrosion potential to more noble direction. The effect of elevation of temperature on the rate of corrosion in devoid of and containing these compounds was studied and some activated thermodynamic parameters were computed.

Síntesis, caracterización y evaluación de la resistencia a la corrosión de recubrimientos híbridos Sol-Gel base TEOS/MPS sobre la aleación AA2050-T8

El presente trabajo tuvo como objetivo sintetizar, caracterizar y evaluar la resistencia a la corrosión de recubrimientos híbridos sol-gel base TEOS/MPS, sintetizados sobre la aleación AA2050-T8 (Al-Cu-Li) bajo diferentes condiciones experimentales de polimerización, tales como solvente y tiempo de envejecimiento, así como diferentes relaciones molares de los precursores inorgánico tetraetoxisilano (TEOS) e híbrido 3-metacriloxipropiltrimetoxisilano (MPS). Se monitoreó la evolución de los soles durante el proceso de envejecimiento mediante espectroscopía infrarroja (FT-IR) y ensayos reológicos. Los recubrimientos se obtuvieron mediante dip-coating y fueron caracterizados a través de microscopía electrónica de barrido (MEB-EDX). La evaluación de la resistencia a la corrosión se realizó mediante ensayos de polarización anódica potenciodinámica, en solución aireada 0,1 M de NaCl. Los resultados obtenidos revelaron que, de los tres solventes evaluados, el etanol es el que permite mejor estabilización del precursor híbrido y favorece el proceso de polimerización de los grupos metacrilato del precursor MPS. Por otra parte, la variación de la relación molar TEOS:MPS conlleva a la obtención de recubrimientos más homogéneos y continuos al incrementar la relación del precursor inorgánico. Finalmente, todos los recubrimientos sintetizados mejoraron la resistencia a la corrosión de la aleación AA2050-T8, en especial los sintetizados bajo la relación TEOS:MPS 80:20.

Effects of inclusions on the resistance to pitting corrosion of S32205 duplex stainless steel

In order to elucidate the effects of inclusions on the resistance to pitting corrosion of S32205 duplex stainless steel, a potentiodynamic anodic polarization test, a weight loss test, a SEM‐EDS analysis, an in situ analysis and ICP analysis are carried out. The results show that the (Ba, Cr, Si, Ca) oxides and (Mn, Si, Cr, Al) oxides are corroded more easily than (Cr, Mn, Al, Ti) oxides, and the equivalent diameter of the former is greater than that of the latter. The pits of dissolved inclusions act as the initial locations of pitting corrosion in the chlorine ions corrosion environment, which accelerates the corrosion of matrix. The proportion of matrix corrosion is higher than inclusions corrosion in the weight loss.